Melasma is a disorder that occurs mainly in women, and produces light-brown symmetric areas of pigmentation on both sides of the face unaccompanied by inflammation. The cause of the disorder has not yet been fully elucidated, however melasma may develop primarily due to polyendrocrine abnormalities by estrogen, adrenal cortex hormone, ACTH, etc., in association with sunlight irradiation, pregnancy, dysfunction of the ovaries, the taking of oral contraceptives, the taking of antiepileptics, etc.
Conventionally, melasma is treated by methods for eliminating endogenous and exogenous causes of the disorder by (1) oral administration of vitamin C or a reduced glutathione agent, (2) elimination of causative agents such as drugs, etc., and (3) avoidance of sunlight irradiation by use of sunscreen (Hyojun Hifukagaku, 4th edition, pp 212-213, edited by Yoshio SATO, issued by Igaku-Shoin). However, the conventional treatment methods do not produce satisfactory effects and are thus unsatisfactory.
Skin dullness is a serious aesthetic problem particularly for women and specifically denotes skin conditions such as loss of skin clarity, skin muddiness due to body waste accumulation, and uneven skin color. Skin dullness may be caused by a combination of various factors, such as skin muddiness or skin shading due to a thickened horny cell layer accompanied by aging, reduced flushness in the skin, pigmentation, lowered skin resilience, yellowing of the skin, dirt such as sweat and sebum, etc.
As described above, since skin dullness is caused by the involvement of various factors, skin dullness cannot be effectively reduced even by substances that have been considered as useful for removing chloasma. Various substances useful for reducing skin dullness have been examined to date, however, at the present time, a substance that can satisfactorily reduce skin dullness has not developed.
It has been reported that purine nucleic acid-related substances exhibit various physiological functions, however it is not known that such substances can improve melasma and reduce skin dullness.
It is known that purine nucleic acid-related substances are hard to formulate. When the substance concerned is blended in a composition to be a concentration such that its effects can be exhibited, the prepared composition is inferior in feeling of use, stability, etc. In particular, the substance is very difficult to add it into an emulsion due to its property of reducing the strength of membranes formed at the oil-water interfaces. Therefore, in order to formulate the substance into an emulsion, such as a milky lotion or cream, it is necessary to develop a method for improve the stability of the emulsion.